WO2010134295A1

WO2010134295A1 - Method of removing the foil shadow of a synchronisation type grid, and radiation image pickup device employing the same

Info

Publication number: WO2010134295A1
Application number: PCT/JP2010/003221
Authority: WO
Inventors: 藤田明徳
Original assignee: 株式会社島津製作所
Priority date: 2009-05-22
Filing date: 2010-05-12
Publication date: 2010-11-25
Also published as: CN102438526B; CN102438526A; US20120063699A1; JPWO2010134295A1; JP5278544B2; US8559754B2

Abstract

The grid foil shadow of a synchronisation type grid can be removed in the following way: an approximate transmission image is found by extracting from a transmission image the detection signal of pixels unaffected by the grid foil shadow and performing interpolation processing (S2 or S2'); a grid foil shadow image is found by finding the difference between the transmission image and the approximate transmission image (S3); a foil shadow reference image is found by averaging the grid foil shadow image in the length direction of the grid foil shadow (S4); and the grid foil shadow is removed by finding the difference between the transmission image and the foil shadow reference image (S5).

Description

Synchronous grid foil shadow removal method and radiation imaging apparatus using the same

The present invention relates to a synchronous grid foil shadow removing method for removing scattered radiation of a radiographic apparatus and a radiographic apparatus using the same, and more particularly to a synchronous grid foil shadow removing method using image processing and the same. The present invention relates to a radiation imaging apparatus.

Conventionally, X-ray imaging apparatuses are equipped with a grid to reduce image quality degradation due to scattered X-rays. However, when a grid is used, a fine vertical pattern due to the shadow of the grid foil is superimposed on the captured image.

In recent years, FPD (Flat Panel Detector) is widely used as an X-ray detector. FPD provides improved spatial resolution and X-ray sensitivity of captured images, and its use is rapidly increasing. However, as the spatial resolution and X-ray sensitivity of the X-ray detector are improved, the grid foil shadow becomes clearer, which becomes a hindrance when reading a captured image. In order to remove this grid foil shadow, Patent Document 1 discloses a method of removing by image processing using frequency conversion.

On the other hand, Patent Document 2 discloses a synchronous grid for FPD. As shown in FIG. 23, the synchronous grid 43 is arranged so that each flat surface of the grid foil 43 a is inclined along a straight line 42 connecting the focal point F of the X-ray source 41 and the X-ray detection surface of the FPD 44. Has been. That is, the grid foil 43a is inclined so as to directly follow the X-ray.

Further, as shown in FIG. 24, the synchronous grid 43 is configured by arranging the grid foil 43 a so that the grid foil shadow is reflected in the center of the detection pixel 47 of the FPD 44. In this way, the positions of the grid foil 43a and the detection pixels 47 are arranged in synchronization. Since the scattered X-rays 45 can be absorbed by the grid foil 43a, noise due to the scattered X-rays 45 can be removed. Further, unlike the conventional grid, the synchronous grid 43 does not use a spacer such as graphite between the grid foils 43a, so that the direct X-ray 46 is not absorbed and the detection efficiency of the direct X-ray 46 is increased. Can do.

The grid foil of the synchronous grid has the same grid ratio although the interval of the grid foil is different from the grid foil of the conventional asynchronous grid. In the synchronous grid, the grid foil gap Gp is longer than that of the asynchronous grid. However, the height A of the grid foil in the direction along the incident direction of the straight X-ray is higher in the synchronous grid than in the asynchronous grid. By doing so, the grid ratio A / Gp of the synchronous grid can be set equal to the grid ratio of the asynchronous grid. As described above, even when the interval between the grid foils Gp in the synchronous grid is longer than that of the conventional one, the noise removal performance of the scattered X-rays 45 can be made the same by increasing the height A of the grid foil. it can.

JP 2000-83951 A JP 2002-257939 A

However, the synchronous grid has a slight distortion of the linear grid foil and a slight shift of the arrangement position due to the production of the grid foil and the structural reason for aligning the grid foil. Moreover, since the height A of the grid foil of the synchronous grid is higher than that of the asynchronous grid, the foil shadow of the synchronous grid is easily affected by the distortion of the grid foil. Due to the distortion and displacement of the grid foil, the grid foil shadow is also distorted. As a result, the measurement value of the foil shadow varies for each grid foil shadow line, and the grid foil shadow is shaded. Thus, even if frequency conversion is used to remove the grid foil shadow, the grid foil shadow of the vertical pattern cannot be sufficiently removed. Artifacts also appear due to grid foil shadows that could not be removed.

Also, in the C-arm X-ray imaging apparatus, heavy-weight X-ray tubes and FPDs are mounted on both ends of the C-arm. As a result, as the C-arm moves such as turning, a slight deflection of the C-arm occurs, and the position of the focal point of the X-ray tube with respect to the FPD slightly moves (about 2 mm at the maximum). When the X-ray tube focus moves, the grid foil shadow on the FPD also moves, so the grid foil shadow cannot be removed sufficiently.

The present invention has been made in view of such circumstances, and it is possible to remove the noise caused by the distortion of the grid foil of the synchronous grid, and the foil shadow removal method of the synchronous grid and the foil shadow removal of the synchronous grid. An object is to provide an apparatus.

In order to achieve such an object, the present invention has the following configuration.
That is, the first invention relates to a grid foil shadow removal method for a radiographic apparatus having a synchronous grid in which grid foils are arranged at regular intervals so that the grid foil shadow is reflected in the center of a pixel for detecting radiation. An approximate fluoroscopic image calculation step for obtaining an approximate fluoroscopic image by extracting a detection signal value of a pixel not affected by the grid foil shadow and performing an interpolation process, and a difference between the fluoroscopic image and the approximate fluoroscopic image A grid foil shadow image calculating step for obtaining a grid foil shadow image and calculating a foil shadow standard image for obtaining a foil shadow standard image by averaging the grid foil shadow image in a length direction of the grid foil shadow; and And a foil shadow removing step of removing the grid foil shadow from the fluoroscopic image based on the foil shadow standard image.

According to the above configuration, an approximate perspective image calculation is performed in a grid foil shadow removal method of a radiation imaging apparatus including a synchronous grid in which grid foils are arranged at regular intervals so that the grid foil shadow is reflected in the center of a pixel for detecting radiation. In step, an approximate perspective image is obtained by extracting a detection signal of pixels not affected by the grid foil shadow from the perspective image and performing an interpolation process. Next, in the grid foil shadow image calculation step, a grid foil shadow image is obtained by obtaining a difference between the perspective image and the approximate perspective image. Further, the foil shadow standard image is obtained by averaging the grid foil shadow image in the length direction of the grid foil shadow in the foil shadow standard image calculating step. In the foil shadow removal step, the grid foil shadow is removed from the fluoroscopic image based on the foil shadow standard image.

Since the grid foil is arranged by being pulled in the foil direction, the change of the grid foil shadow in the length direction of the grid foil is relatively small. On the other hand, each grid foil has an error due to a shape or twist, and a minute arrangement direction or position error. Even if there is non-uniformity in the size of the grid foil shadow for each grid foil, the grid foil shadow is averaged in the length direction of the grid foil shadow, and the grid foil is obtained from the perspective image based on the averaged foil shadow standard image. Remove shadows. By performing the averaging, it is possible to remove amplifier noise, quantum noise, and the like that are randomly mixed for each pixel. In addition, an interpolation error included in calculating the approximate fluoroscopic image can be removed. As described above, since the spacer is not sandwiched between the grid foils, it is possible to remove the grid foil shadows without causing artifacts even in a synchronous grid in which it is difficult to accurately arrange the grid foils.

Further, it is preferable that the foil shadow removal step removes the grid foil shadow from the fluoroscopic image based on a difference between the fluoroscopic image and the foil shadow standard image. By subtracting the foil shadow standard image from the fluoroscopic image, the grid foil shadow can be easily removed from the fluoroscopic image.

Further, the foil shadow standard image averaged by the foil shadow standard image calculating step is extracted for each row, and is extracted for each number of pixels within a predetermined interval where the grid foil is arranged, and row data is created. A smoothing step of smoothing the row data and replacing the original foil shadow standard image, wherein the foil shadow removal step includes the difference between the fluoroscopic image and the smoothed foil shadow standard image. It is preferable to remove the grid foil shadow from the surface.

According to the above configuration, the row shadow data obtained by extracting and dividing the foil shadow standard image averaged by the foil shadow standard image calculating step for each row and for each number of pixels within a predetermined interval where the grid foil is arranged. Since it has a smoothing step to create and smooth this row data and replace it with the original foil shadow standard image, the foil shadow standard image that could not be smoothed in the row direction is stored in the pixels arranged between the grid foils. Smoothing can be performed for each row data divided by the number. Thus, amplifier noise and quantum noise can be further removed. The foil shadow removal step obtains a difference between the fluoroscopic image and the smoothed foil shadow standard image and removes the grid foil shadow from the fluoroscopic image.

Further, the foil shadow removing step calculates an error component image calculating step for obtaining an error component image by calculating a difference between the grid foil shadow image and the foil shadow standard image, and calculating a difference between the fluoroscopic image and the error component image. A foil shadow distortion removed image calculating step for obtaining a foil shadow distortion removed image and a frequency conversion processing step for performing a frequency conversion process on the foil shadow distortion removed image to remove the grid foil shadow may be provided.

According to the above configuration, the error component image is obtained by obtaining the difference between the grid foil shadow image and the foil shadow standard image in the error component image calculation step. In the foil shadow distortion removed image calculation step, a difference between the fluoroscopic image and the error component image is obtained to obtain a foil shadow distortion removed image. In the frequency conversion processing step, frequency conversion processing is performed on the foil shadow distortion-removed image to remove grid foil shadows. By removing the error component image that is the difference between the averaged foil shadow standard image and the foil shadow image from the fluoroscopic image, the error component for each grid foil is removed, so the remaining grid foil shadow is subjected to frequency conversion processing. Can be removed. Even in a synchronous grid in which it is difficult to accurately arrange the grid foils, the frequency conversion process can be performed to remove the grid foil shadows.

Further, the foil shadow standard image averaged by the foil shadow standard image calculating step is extracted for each row, and is extracted for each number of pixels within a predetermined interval where the grid foil is arranged, and row data is created. A smoothing step of smoothing the row data and replacing the original foil shadow standard image, wherein the error component image calculating step calculates a difference between the grid foil shadow image and the smoothed foil shadow standard image. Then, an error component image may be obtained.

According to the above configuration, the row shadow data obtained by extracting and dividing the foil shadow standard image averaged by the foil shadow standard image calculating step for each row and for each number of pixels within a predetermined interval where the grid foil is arranged. Since it has a smoothing step to create and smooth this row data and replace it with the original foil shadow standard image, the foil shadow standard image that could not be smoothed in the row direction is stored in the pixels arranged between the grid foils. Smoothing can be performed for each row data divided by the number. Thus, amplifier noise and quantum noise can be further removed. The error component image calculation step obtains a pixel component image by obtaining a difference between the grid foil shadow image and the smoothed foil shadow standard image.

Further, either the normal correction mode in which the movement of the foil shadow between the pixels is not corrected or the special correction mode in which the movement of the foil shadow between the pixels is corrected is selected based on the set SID amount and the movement amount of the C-arm. When the normal correction mode is selected in the image processing mode selection step and the image processing mode selection step, the approximate fluoroscopic image calculation step detects all pixels other than the pixels arranged in advance so that the grid foil shadow is reflected. When the signal is extracted and interpolation processing is performed, and the special correction mode is selected in the image processing mode selection step, the approximate perspective image calculation step is performed between the grid foils where the foil shadow does not appear even if the foil shadow moves. It is preferable to perform an interpolation process by extracting a detection signal of a pixel located at the center of the pixel.

According to the above configuration, in the image processing mode selection step, the normal correction mode is selected when the foil shadow does not move across the pixels due to the SID amount input and the movement amount of the C-shaped arm, and the foil shadow is When moving across pixels, the special correction mode for correcting the movement of the foil shadow between the pixels is selected. When the normal correction mode is selected, the approximate perspective image calculation step detects all pixels other than the pixels previously arranged so that the grid foil shadow is reflected as pixels not affected by the grid foil shadow. The signal is extracted and interpolation processing is performed. On the other hand, when the special correction mode is selected, the pixel located at the center between the grid foils where the foil shadow does not appear even if the foil shadow moves is regarded as a pixel not affected by the grid foil shadow. The detection signal is extracted and interpolation processing is performed. Thus, even when the foil shadow does not move across the pixels or when it moves, the approximate perspective image can be calculated by appropriately performing the interpolation process.

According to a second aspect of the present invention, in the radiation imaging apparatus, radiation irradiating means for irradiating a subject with radiation, radiation detecting means for arranging pixels for detecting radiation transmitted through the subject in a two-dimensional array, and grid foil Interpolation is performed by extracting a set of pixels that are not affected by the grid foil shadow from a synchronous grid arranged at regular intervals so that the shadow is reflected in the center of the pixel and a fluoroscopic image detected through the subject. An approximate perspective image calculation unit that calculates an approximate perspective image, a grid foil shadow image calculation unit that obtains a grid foil shadow image by obtaining a difference between the perspective image and the approximate perspective image, and a grid foil shadow image A foil shadow standard image calculating unit for obtaining a grid foil shadow standard image by averaging in the length direction of the foil shadow, and removing the grid foil shadow from the fluoroscopic image based on the grid foil shadow standard image Characterized in that a foil shadow removed image calculating unit for obtaining a subtracted image.

According to the above configuration, in the radiographic apparatus, the radiation is irradiated to the subject by the radiation irradiating means, and the radiation that has passed through the subject is detected by the radiation detecting means in which the pixels for detecting the radiation are arranged in a two-dimensional array, The synchronous grid is arranged at regular intervals so that the grid foil shadow is reflected in the center of the pixel. The approximate fluoroscopic image calculation unit calculates an approximate fluoroscopic image by extracting a pixel set that is not affected by the grid foil shadow from the fluoroscopic image detected through the subject and performing an interpolation process. The grid foil shadow image calculation unit obtains a grid foil shadow image by obtaining a difference between the perspective image and the approximate perspective image. The foil shadow standard image calculation unit obtains a grid foil shadow standard image by averaging the grid foil shadow image in the length direction of the grid foil shadow. The foil shadow removed image calculation unit obtains a foil shadow removed image by removing the grid foil shadow from the fluoroscopic image based on the grid foil shadow standard image.

From this, even if the grid foil shadow is not uniform, the grid foil shadow is averaged in the length direction of the grid foil shadow, and the grid foil shadow is removed from the fluoroscopic image based on the averaged foil shadow standard image. Even if there is non-uniformity in the size of the grid foil shadow for each grid foil, the grid foil shadow is averaged in the length direction of the grid foil shadow, and the grid foil is obtained from the perspective image based on the averaged foil shadow standard image. Remove shadows. By performing averaging, it is possible to remove amplifier noise, quantum noise, and the like that are randomly mixed for each pixel. In addition, an interpolation error included in calculating the approximate fluoroscopic image can be removed. Even in a synchronous grid in which it is difficult to accurately arrange the grid foil, the grid foil shadow can be removed without causing artifacts.

Moreover, it is preferable that the foil shadow removal image calculation unit obtains the foil shadow removal image based on a difference between the fluoroscopic image and the grid foil shadow standard image. According to this configuration, the foil shadow removed image can be easily obtained by subtracting the foil shadow standard image from the fluoroscopic image.

Further, the foil shadow removal image calculation unit obtains an error component image by obtaining a difference between the grid foil shadow image and the grid foil shadow standard image, the perspective image, and the error component image. A foil shadow distortion-removed image calculating unit that obtains a foil shadow distortion-removed image by obtaining a difference between them, and a frequency conversion processing unit that performs a frequency conversion process on the foil shadow distortion-removed image to remove a grid foil shadow. .

The error component image calculation unit obtains an error component image by obtaining a difference between the grid foil shadow image and the grid foil shadow standard image. The foil shadow distortion removed image calculating unit obtains a foil shadow distortion removed image by obtaining a difference between the fluoroscopic image and the error component image. The frequency conversion processing unit performs frequency conversion processing on the corrected perspective image to remove the grid foil shadow. As a result, even if the grid foil shadow is not uniform, the grid foil shadow is averaged in the length direction of the grid foil shadow, and the error component image that is the difference between the averaged foil shadow standard image and the foil shadow image is seen through. By removing from the image, it is possible to obtain a perspective image having a uniform grid foil shadow, and to remove the remaining grid foil shadow by subjecting this perspective image to frequency conversion processing. Even in a synchronous grid in which it is difficult to uniformly form the shape and arrangement of each grid foil, the frequency conversion process can be performed to remove the grid foil shadow.

Further, an input unit for inputting and setting the SID amount and the movement amount of the C-type arm, and a correction for selecting either the normal correction mode or the special correction mode based on the set and inputted SID amount and the movement amount of the C-type arm. A mode selection unit, and when the normal correction mode is selected as the correction mode, the approximate fluoroscopic image calculation unit extracts detection signal values of all pixels other than pixels arranged in advance so that a grid foil shadow is reflected. When the special correction mode is selected as the correction mode, the detection signal value of the pixel located at the center between the grid foils where the foil shadow does not appear even if the foil shadow moves is interpolated. It is preferable to carry out the treatment.

According to the above configuration, the SID amount and the C-arm movement amount are input and set at the input unit. In the correction mode selection unit, either the normal correction mode or the special correction mode is selected based on the set and input SID amount and the C-arm movement amount. When the normal correction mode is selected as the correction mode, the approximate fluoroscopic image calculation unit extracts the detection signal values of all the pixels other than the pixels previously arranged so that the grid foil shadow is reflected, and performs the interpolation process. When the special correction mode is selected as the correction mode, the detection signal value of the pixel located at the center between the grid foils where the foil shadow does not appear even if the foil shadow moves is extracted and interpolation processing is performed. Thus, even when the foil shadow does not move across the pixels or when it moves, the approximate perspective image can be calculated by appropriately performing the interpolation process.

Further, the foil shadow standard image calculated by the foil shadow standard image calculation unit is extracted and divided for each number of pixels in which the grid foil is arranged at regular intervals for each row, and the row data is created. It is preferable to provide a smoothing unit that smoothes data and replaces the original foil shadow standard image.

According to the above configuration, the smoothing unit extracts and divides the foil shadow standard image calculated by the foil shadow standard image calculation unit for each number of pixels within a predetermined interval in which the grid foil is arranged for each row. Line data is created, and the line data is smoothed and replaced with the original foil shadow standard image. Accordingly, it is possible to divide line data having a relatively large change into a plurality of smooth line data. As a result, the foil shadow standard image that cannot be smoothed in the row direction can be smoothed for each row data divided by the number of pixels in which the grid foil is arranged at a constant interval. In this way, by correcting the variation for each grid foil shadow, a foil shadow standard image in which amplifier noise and quantum noise are further suppressed can be calculated.

Further, it is preferable that the synchronous grid and the radiation detector are arranged in advance so that a grid foil shadow is reflected every four pixels. According to this configuration, the synchronous grid and the radiation detector are arranged so that the grid foil shadow is projected every four pixels in advance. As a result, even if the grid foil shadow moves, the movement of the grid foil shadow can be accommodated in the pixels adjacent to the pixels that are arranged so that the grid foil is reflected in advance. Can do.

According to the synchronous grid foil shadow removing method and synchronous grid foil shadow removing apparatus according to the present invention, the synchronous grid foil shadow removing method and the synchronous grid foil shadow removing method capable of removing noise caused by the distortion of the grid foil of the synchronous grid and A synchronous grid foil shadow removing apparatus can be provided.

1 is an overall view of an X-ray fluoroscopic apparatus according to an embodiment. It is a schematic sectional drawing of the grid of the X-ray fluoroscopic apparatus which concerns on an Example. It is a perspective view of the grid foil of the X-ray fluoroscopic apparatus which concerns on an Example. It is a schematic sectional drawing of the grid and FPD of the X-ray fluoroscopic apparatus which concerns on an Example. It is explanatory drawing of SID of the X-ray fluoroscopic apparatus which concerns on an Example. 1 is a schematic view of an X-ray fluoroscopic apparatus according to an embodiment. It is explanatory drawing explaining the movement of the X-ray focus of the X-ray fluoroscopic apparatus which concerns on an Example. It is explanatory drawing explaining the movement of the X-ray focus of the X-ray fluoroscopic apparatus which concerns on an Example. It is explanatory drawing explaining the movement of the foil shadow on the pixel of FPD which concerns on an Example. FIG. 3 is a block diagram illustrating a configuration of an image processing unit according to the first embodiment. It is explanatory drawing which shows the pixel of FPD on which the foil shadow based on an Example was reflected. It is explanatory drawing which shows the pixel of FPD on which the foil shadow based on an Example was reflected. It is explanatory drawing which shows the detection value of the pixel in which the foil shadow which concerns on an Example is reflected. It is explanatory drawing which shows the detection value of the pixel in which the foil shadow which concerns on an Example is reflected. It is a flowchart figure which shows the flow of the foil shadow correction process which concerns on Example 1. FIG. FIG. 10 is a block diagram illustrating a configuration of an image processing unit according to a second embodiment. It is a flowchart figure which shows the flow of the foil shadow correction process which concerns on Example 2. FIG. FIG. 10 is a block diagram illustrating a configuration of an image processing unit according to a third embodiment. FIG. 10 is an explanatory diagram illustrating image processing according to a third embodiment. It is a flowchart figure which shows the flow of the foil shadow correction process which concerns on Example 3. FIG. FIG. 10 is a block diagram illustrating a configuration of an image processing unit according to a fourth embodiment. It is a flowchart figure which shows the flow of the foil shadow correction process which concerns on Example 4. FIG. It is a schematic sectional drawing of the grid of the X-ray fluoroscopic apparatus which concerns on a prior art example. It is a schematic sectional drawing of the grid of the X-ray fluoroscopic apparatus which concerns on a prior art example.

DESCRIPTION OF SYMBOLS 1 ... X-ray imaging apparatus 2 ... X-ray tube 3 ... Synchronous grid 4 ... FPD
5 ... C-type arm 12 ... Image processing section
DESCRIPTION OF SYMBOLS 19 ... Correction mode selection part 20 ... 1st approximate image calculation part 21 ... 2nd approximate image calculation part 22 ... Foil shadow image calculation part 23 ... Foil shadow standard image calculation part 24 ... Subtraction part 33 ... Foil shadow removal image calculation part 34 ... Error component image calculation unit 35 ... Foil shadow distortion removed image calculation unit 36 ... Frequency conversion processing unit 31 ... Smoothing unit 37 ... Smoothing unit DU ... X-ray detection pixel

Embodiment 1 of the present invention will be described below with reference to the drawings.
1 is an overall view of the X-ray fluoroscopic apparatus, FIG. 2 is a schematic sectional view of a grid, FIG. 3 is a perspective view of a grid foil, and FIG. 4 is a schematic sectional view of a grid and an FPD.

As shown in FIG. 1, an X-ray fluoroscopic apparatus 1 includes an X-ray tube 2 that irradiates a subject M with X-rays, and a synchronous grid that removes scattered X-rays transmitted through the subject M. 3 and a flat detector (flat panel detector: hereinafter referred to as FPD) 4 for detecting transmitted X-rays from which scattered X-rays have been removed. The X-ray tube 2, the synchronous grid 3 and the FPD 4 are attached to both ends of the C-type arm 5 so as to face each other. The C-type arm 5 is moved by a C-type arm moving mechanism 6, and the movement amount of the C-type arm moving mechanism 6 is controlled by a C-type arm movement control unit 7. The X-ray tube 2 corresponds to the radiation irradiation means in the present invention, and the FPD 4 corresponds to the radiation detection means in the present invention.

The C-arm 5 is configured to be vertically movable (R1) with respect to the top plate 8 on which the subject M is placed. Further, the arm support 9 that supports the C-shaped arm 5 is attached to be rotatable (R2) around a vertical axis. The C-arm 5 is rotatable around a horizontal axis (R3) and is attached to the arm support 9 so as to be movable in an arcuate shape (R4). Further, in order to adjust the SID (Source Image Distance) that is the distance between the X-ray tube 2 and the synchronous grid 3 and the FPD 4, the C-type arm moving mechanism 6 causes the synchronous grid 3 and the FPD 4 to move in the vertical direction (R5). It is movable.

In addition, the X-ray fluoroscopic apparatus 1 also receives an X-ray tube control unit 10 that controls a tube voltage and a tube current output to the X-ray tube 2 and an analog X-ray detection signal output from the FPD 4. An A / D converter 11 that converts a digital X-ray detection signal, an image processing unit 12 that performs various image processing from the digital X-ray detection signal, a main control unit 13 that supervises these components, An input unit 14 in which a photographer performs various input settings, a monitor 15 that displays an X-ray diagnostic operation screen and an image-processed X-ray transmission image, and a storage unit that stores an X-ray transmission image and other imaging data 16 etc. are provided.

The main control unit 13 includes a central processing unit (CPU). The input unit 14 includes a pointing device represented by a mouse, a keyboard, a joystick, a trackball, a touch panel, and the like. The photographer can set and input the amount of movement of the SID and the C-type arm through the input unit 14. Examples of the monitor 15 include a liquid crystal display device or a CRT display, and examples of the storage unit 16 include a hard disk and a memory.

As shown in FIGS. 2 and 3, the synchronous grid 3 is disposed so as to cover the X-ray detection surface of the FPD 4. The synchronous grid 3 includes a grid foil 3a that absorbs strip-shaped X-rays extending in the longitudinal (Y) direction. Each flat surface of the grid foil 3 a is disposed so as to be inclined along a straight line connecting the focal point F of the X-ray source of the X-ray tube 2 and the X-ray detection surface of the FPD 4. That is, the grid foil 3a is inclined so as to follow the direct transmission X-ray Dx. The synchronous grid 3 is an array of grid foils 3 a so that a grid foil shadow (hereinafter simply referred to as a foil shadow) is reflected in the center of the X-ray detection pixel DU of the FPD 4.

As shown in FIGS. 3 and 4, the grid foils 3a are arranged at predetermined intervals in the lateral (X) direction, and the arrangement pitch Gp is 400 μm in the first embodiment. This arrangement pitch Gp is appropriately designed in synchronization with the width W _DU of the X-ray detection pixel DU of the FPD 4. That is, the foil shadow of the grid foil 3a is arranged at a predetermined pixel interval on the X-ray detection pixel DU at the C-arm standard position in the reference SID. In the first embodiment, since the width W _DU of the X-ray detection pixel DU is 100 μm, a foil shadow is projected at a ratio of one in four in the horizontal direction with respect to the X-ray detection pixel DU.

The grid foil 3a is made of a simple substance such as molybdenum, tungsten, lead, or tantalum, or an alloy containing these as a main component. For this metal, it is preferable to select a material having a large atomic number and a large X-ray absorption, and usually has a thickness of 20 to 50 μm. The grid foil 3a is manufactured by rolling, cutting, or the like. However, since it is a heavy metal or an alloy of heavy metals as described above, it is very difficult to strictly determine the shape uniformity such as the thickness and width of the grid foil 3a. is there. This non-uniformity of the shape of the grid foil 3a causes variations in the detected value of the foil shadow.

In the FPD 4, for example, 2000 × 2000 X-ray detection pixels DU that convert X-rays into charge signals are arranged in a two-dimensional array. The X-ray detection pixel DU includes an X-ray detection element that generates a charge signal when irradiated with X-rays.

SID is a perpendicular distance between the focal point of the X-ray source in the X-ray tube 2 and the FPD 4. If the SID is short, an enlarged fluoroscopic image of the subject M can be obtained, and if the SID is long, a wide-angle fluoroscopic image of the subject M can be obtained. In other words, the perspective image can be adjusted by adjusting the SID. In the first embodiment, the case where the SID is 1000 mm is set as the reference SID. At the standard position of the C-arm at the time of the reference SID, the grid foil 3a and the FPD 4 are positioned so that the foil shadow of the synchronous grid 3 is projected on the X-ray detection pixel of the FPD 4 in a ratio of one to four in the horizontal direction. It is matched. Also, the C-arm standard position is a three-dimensionally determined positional relationship with respect to the bed, the top plate 8 and the examination room as shown in FIG. This is the default position. This position is a standard position where it is considered that there is no deflection of the C-type arm 5 in order to align the synchronous grid 3 and the FPD 4 at this position.

¡When this SID is changed, the foil shadow on the X-ray detection surface moves. As shown in FIG. 5, for example, when the SID is extended beyond the reference SID, the foil shadow at the center of the FPD 4 is not significantly affected, but the foil shadow moves to the inside of the FPD 4 as it approaches the side edge of the FPD 4. To do. Conversely, if the SID is shorter than the reference SID, the foil shadow moves to the outside of the FPD 4.

The movement of the foil shadow also occurs when the C-arm 5 is moved such as turning. When the C-arm 5 is turned as shown in FIG. 6, deflection is inevitably generated in the C-arm 5 due to the rigidity of the C-arm 5. Due to this deflection, when the X-ray focal point of the X-ray tube 2 moves, the foil shadow also slightly moves in the reference SID. The amount of movement of the X-ray focal point due to the deflection of the C-arm 5 is at most about 2 mm. For example, as shown in FIG. 7, when the X-ray focal point F in the X-ray tube 2 moves slightly, the straight line connecting the X-ray focal point F and the detection surface of the FPD 4 and the inclination angle of the flat surface of the grid foil 3a It will not match. As a result, the foil shadow moves minutely on the X-ray detection surface. As shown in FIG. 8, when the SID is 1000 mm and the distance between the synchronous grid 3 and the FPD 4 is 20 mm, the movement amount of the foil shadow is the distance from the focal point F of the X-ray tube 2 to the synchronous grid 3 The ratio of the distance from the synchronous grid 3 to the FPD 4 is about 50: 1. Thus, when the X-ray source moves 2 mm, the foil shadow of the grid foil 3 a moves about 40 μm on the detection surface of the FPD 4.

When the thickness of the grid foil 3a is 30 μm and the width of the foil shadow is 30 μm, the foil shadow is set so that the foil shadow is positioned at the center of the pixel when the X-ray tube focus is not moved in the reference SID. There is a margin of 35 μm from the shadow to the adjacent pixel. However, as described above, when the foil shadow moves by 40 μm, as shown in FIG. 9, the foil shadow protrudes from the pixel arranged so that the foil shadow is projected in advance to the adjacent pixel.

In this way, there are two possible cases: when the foil shadow is in the synchronized pixel so that it is reflected in advance, and when the foil shadow straddles the pixel or moves completely to the pixel next to the synchronized pixel. . Therefore, the image processing unit 5 performs foil shadow correction suitable for each case.

Next, refer to FIG. FIG. 10 is a block diagram illustrating a configuration of the image processing unit. The image processing unit 5 includes a LOG conversion unit 17 that performs LOG conversion on the digital X-ray detection signal converted by the A / D converter 11, and an image that stores several LOG-converted X-ray detection signals for several sheets. Memory unit 18, correction mode selection unit 19 for selecting a foil shadow correction mode based on the SID amount set in the input unit 14 or the movement amount of the C-type arm 5, and the X-ray detection image stored in the image memory unit 18 A first approximate fluoroscopic image calculation unit 20 and a second approximate fluoroscopic image calculation unit 21 that select a set of pixels not affected by the foil shadow and calculate an approximate fluoroscopic image of the subject M, and an X-ray detection image and an approximation A foil shadow image calculation unit 22 that calculates a grid foil shadow image based on a difference from the perspective image, a foil shadow standard image calculation unit 23 that calculates a grid foil shadow standard image by averaging the grid foil shadow image, and an image memory Part 18 And a subtracting unit 24 for calculating a foil shadow removed X-ray detection image by calculating a difference between the stored X-ray detection image and the grid shadow standard image.

The LOG converter 17 performs LOG conversion on the digital X-ray detection signal converted by the A / D converter 11. As a result, the X-ray detection signal can be calculated as a linear sum, and subsequent calculations can be simplified.

The image memory unit 18 stores a number of X-ray detection images composed of X-ray detection signals that have been LOG-converted by the LOG conversion unit 17. The image memory unit 18 also functions as a buffer.

The correction mode selection unit 19 selects the normal correction mode or the special correction mode as the foil shadow correction mode. This selection is performed based on the SID amount input and set in the input unit 14 sent via the main control unit 13 and the movement amount of the C-type arm 5. Here, the amount of movement is the amount of movement of the C-arm 5 from the C-arm standard position.

The normal correction mode is a correction mode that is selected when the SID is the reference SID and the movement of the foil shadow due to the deflection of the C-arm 5 can be ignored. That is, this is a correction mode in the case where the foil shadow is not projected from the pixels arranged in advance so that the foil shadow is projected. As shown in FIG. 11, if a pixel arranged in advance so that a foil shadow is reflected is P _{4n + 1} in the row direction, that is, the horizontal direction (where n is an integer of 0 or more), it is represented by P _{4n + 1 every} four pixels. A foil shadow is always projected on the pixel. Further, since the shape of the grid foil 3a is not strictly uniform and the arrangement of the grid foil 3a is also slightly shifted, the width of the foil shadow varies as shown by the foil shadow 27 and the foil shadow 28. However, a foil shadow is not reflected on the pixels represented by P _{4n + 2,} P _{4n + 3,} and P _{4n + 4} next to the pixel other than the pixel P _{4n + 1} . Therefore, foil shadow correction is performed using a pixel set obtained by extracting the pixels P _{4n + 2,} P _{4n + 3,} and P _{4n + 4,} which are _three pixel sets between the foil shadows. This correction method is the normal correction mode.

In the special correction mode, when the SID is moved from the reference SID or when the focus of the X-ray tube is moved by the deflection of the C-arm 5, a pixel that is arranged in advance so as to show a foil shadow is projected to the adjacent pixel. This is a correction method in the case where the image is reflected up to. Assuming that a pixel pre-arranged so that a foil shadow is reflected is P _{4n + 1} in the horizontal direction (where n is an integer of 0 or more), the foil shadow is a pixel due to SID movement or deflection of the C-arm 5 as shown in FIG. Move from the top of P _{4n + 1} . For example, the foil shadow 29 is reflected across the pixel P _{4n + 1} and the horizontally adjacent pixel P _{4n + 2} . Further, the foil shadow 30 has completely moved from the element P _{4 (n + 1) +1} to the pixel P _{4n + 4} . Thus, it is pixel P4n _{+ 3} located in the center between the pixels previously arrange | positioned so that a foil shadow may not be reflected by movement of about 40 micrometers reliably. Therefore, the foil shadow correction is performed using a pixel set obtained by extracting the pixel P _{4n + 3} located at the center between the pixels arranged so that the foil shadow is projected in advance. This correction method is a special correction mode.

When the correction mode selection unit 19 selects the normal correction mode, the first approximate fluoroscopic image calculation unit 20 includes pixels P _{4n + 2} that are not affected by the foil shadow from the X-ray detection image stored in the image memory unit 18 _. A pixel set from which P _{4n + 3} and P _{4n + 4} are extracted is selected to calculate a first approximate fluoroscopic image of the subject M. As described above, in selecting a pixel set that is not affected by the foil shadow, all the pixels other than the pixel P _{4n + 1} in which the foil shadow is predetermined are selected.

As shown in FIG. 13A, when X-ray imaging is performed without placing the subject M on the top board 8, the X-ray detection signal value at the pixel P _{4n + 1} where the foil shadow of the grid foil 3a is projected. (● mark) is a value that is reduced by about 20% as shown in FIG. 13B from the X-ray detection signal values (Δ mark and □ mark) in other pixels.

Next, as shown in FIG. 14A, when the subject M is placed on the top board 8 and X-ray imaging is performed, the pixel P on which the foil shadow of the grid foil 3a is projected is the same as described above. The X-ray detection signal value (● mark) at _{4n + 1} is a value that is lower than the X-ray detection signal values (Δ mark and □ mark) at other pixels as shown in FIG. Therefore, a pixel set obtained by extracting the pixels P _{4n + 2,} P _{4n + 3,} and P _{4n + 4} which are not affected by the foil shadow is selected, and the grid is determined from the X-ray detection signal values (Δ mark and □ mark) of these pixel sets. The X-ray detection signal value (● mark) at the pixel P _{4n + 1} where the foil shadow of the foil 3a is reflected is interpolated. In this interpolation method, the fluoroscopic image of the subject M can be accurately estimated by cubic interpolation such as quadratic interpolation or cubic spline method. A first approximate image that is a fluoroscopic image estimated in this way can be calculated. The first approximate image calculated by the interpolation includes an interpolation error.

When the correction mode selection unit 19 selects the special correction mode, the second approximate fluoroscopic image calculation unit 21 selects a pixel set that is not affected by the foil shadow from the X-ray detection image stored in the image memory unit 18. Then, the second approximate fluoroscopic image of the subject M is calculated. In the special correction mode, the foil shadow may also be moved to the pixel P _{4n + 2} or P _{4 (n−1) +4} adjacent to the pixel P _{4n + 1 on which} the foil shadow of the grid foil 3a is projected. Therefore, the second approximate fluoroscopic image calculation unit 21 selects pixel sets obtained by extracting the pixels P _{4n + 3 in} which the foil shadow does not appear even if the foil shadow moves due to the movement of the SID or the C-type arm 5, and these pixel sets From the X-ray detection signal value (Δ mark), the X-ray detection signal value (● in the pixel P _{4n + 1 in which the} foil shadow of the grid foil 3a is reflected and the pixel P _{4n + 2} or P _{4n + 4 to} which the foil shadow may move. Interpolate marks and □ marks). This interpolation method can accurately estimate a fluoroscopic image of the subject M by cubic interpolation such as a cubic spline method. A second approximate image that is a perspective image estimated in this manner can be calculated. The second approximate image calculated by interpolation includes an interpolation error.

In addition, when referring to both a 1st approximate fluoroscopic image and a 2nd approximate fluoroscopic image, it describes only as an approximate fluoroscopic image. The first approximate fluoroscopic image calculation unit and the second approximate fluoroscopic image calculation unit correspond to the approximate fluoroscopic image calculation unit in the present invention.

The foil shadow image calculation unit 22 calculates a grid foil shadow image based on the difference between the X-ray detection image and the approximate fluoroscopic image. That is, since an image composed of X-ray detection signals corresponding to the amount of foil shadows superimposed and reduced is calculated, a grid foil shadow image that is an image representing only the foil shadows can be obtained. Since the foil shadow is formed in the vertical direction along the grid foil 3a, the grid foil shadow image is also image data in which detection values are arranged in the vertical direction. Since the grid foil shadow image is calculated based on the approximate perspective image including the interpolation error, the grid foil shadow image also includes the interpolation error.

The foil shadow standard image calculation unit 23 calculates a grid foil shadow standard image by averaging the grid foil shadow images in which the detection values are arranged in the vertical direction in the vertical direction. That is, as shown in FIGS. 11 and 12, correction is performed by averaging variations in the detected value of the foil shadow caused by the nonuniformity of the shape of the foil shadow. For example, the average value of the detection values (pixel values) of the detection pixels in the upper and lower 30 pixels of the correction target pixel is calculated, and this average value is replaced with the pixel value of the correction target pixel. A grid foil shadow standard image can be calculated by performing this process for all detection pixels. Further, by averaging the grid foil shadow image in the longitudinal direction, that is, the length direction of the foil shadow, the interpolation error included in the grid foil shadow image can be removed.

The subtraction unit 24 calculates a foil shadow removal perspective image based on the difference between the X-ray detection image stored in the image memory unit 18 and the grid foil shadow standard image. By removing the standardized foil shadow from the X-ray detection image, a fluoroscopic image of the subject from which the influence of the interpolation error has been removed can be acquired. The subtraction unit 24 corresponds to the foil shadow removal image calculation unit in the present invention.

The fluoroscopic image of the subject from which the foil shadow has been removed by the subtracting unit 24 is displayed on the monitor 15 or stored in the storage unit 16 via the main control unit 13.

Next, the operation when X-ray fluoroscopic imaging is performed according to the first embodiment will be described.

First, the photographer sets the SID amount and the movement amount of the C-arm 5 in the input unit 14. Accordingly, the main control unit 13 transfers the set SID amount and the movement amount of the C-type arm 5 to the C-type arm movement control unit 7. The C-type arm movement control unit 7 causes the C-type arm moving mechanism 6 to move the C-type arm 5 by reflecting the set amounts. Next, when an instruction to start X-ray imaging is given to the input unit 14, the main control unit 13 controls the X-ray tube control unit 10 and the FPD 4. The X-ray tube control unit 10 applies a tube voltage or a tube current to the X-ray tube 2 based on an instruction from the main control unit 13, and the subject M is irradiated with X-rays from the X-ray tube 2. The X-rays transmitted through the subject M are removed from the scattered grid 3 by the synchronous grid 3, enter the FPD 4, and are detected by the X-ray detection pixel DU. The X-ray detection signal detected by the X-ray detection pixel DU is converted from analog to digital by the A / D converter 11. The X-ray detection signal converted to digital is transferred to the image processing unit 12 and is LOG converted by the LOG conversion unit 17. The LOG-converted X-ray detection signal is stored as an X-ray detection image in the image memory unit 18.

Next, the foil shadow is corrected according to the flowchart shown in FIG. Note that the foil shadow is corrected in the normal correction mode during normal shooting. Here, the normal photographing means a case where the SID is the reference SID and the deflection of the C-arm 5 does not affect the foil shadow. The reference SID is 1000 mm in the first embodiment, but may be set as appropriate. When the SID is moved from the reference SID and when the deflection of the C-arm cannot be ignored, the foil shadow is corrected in the special correction mode.

Step S1 (correction mode selection)
The SID amount set by the photographer in the input unit 14 and the movement setting amount of the C-arm 5 are sent to the correction mode selection unit 19 in the image processing unit 5 via the main control unit 13. Based on these pieces of information, the correction mode selection unit 19 selects the normal correction mode or the special correction mode. The normal correction mode is selected when the SID amount and the movement amount of the C-arm 5 do not affect the foil shadow, that is, when the SID amount and the movement of the C-shaped arm 5 are not included in the pixels set so that the foil shadow is projected in advance. Further, when the SID amount and the movement amount of the C-shaped arm 5 affect the foil shadow, that is, when it protrudes from a pixel set so that the foil shadow is projected in advance, the special correction mode is selected.

Step S2 (first approximate fluoroscopic image calculation)
When the normal correction mode is selected in step S1, the first approximate fluoroscopic image calculation unit 20 selects a pixel set obtained by extracting three detection pixels between the foil shadows in which the foil shadow is not reflected. Further, the first approximate fluoroscopic image obtained by seeing through the subject M is calculated by interpolating the detection values of the detection pixels not selected from the pixel values of the pixel set.

Step S2 ′ (second approximate fluoroscopic image calculation)
When the special correction mode is selected in step S1, the second approximate perspective image calculation unit 21 selects a pixel set obtained by extracting the detection pixel at the center between the foil shadows where the foil shadow is not reflected. Further, the second approximate fluoroscopic image obtained by seeing through the subject M is calculated by interpolating the detection values of the detection pixels not selected from the pixel values of the pixel set.

Step S3 (calculate foil shadow image)
In the foil shadow image calculation unit 22, the X-ray detection image stored in the image memory unit 18, the approximate fluoroscopic image calculated by the first approximate fluoroscopic image calculation unit 20 or the second approximate fluoroscopic image calculation unit 21, and A grid foil shadow image is calculated from the difference between the two. That is, since an image consisting only of the X-ray detection signal from the detection pixel that becomes the shadow of the foil shadow is calculated, a grid foil shadow image can be obtained.

Step S4 (calculate foil shadow standard image)
The foil shadow standard image calculation unit 23 calculates the grid foil shadow standard image by averaging the grid foil shadow images in which the detection values are arranged in the vertical direction in the vertical direction. Since each grid foil 3a is pulled and held in the vertical direction, that is, the foil direction, the change of the foil shadow in the length direction of the grid foil 3a is relatively small. Amplifier noise and quantum noise can be corrected by averaging the foil shadows. For example, an average value of detection values of detection pixels of several tens of pixels above and below the pixel to be corrected is calculated, and this average value is replaced with a pixel value to be corrected. A grid foil shadow standard image is calculated by performing this process for all the detection pixels.

Step S5 (calculate foil shadow removal image)
The subtraction unit 24 calculates a foil shadow removal perspective image by subtracting the X-ray detection image from the grid foil shadow standard image. Thus, a fluoroscopic image of the subject from which the foil shadow has been removed can be acquired. The fluoroscopic image of the subject from which the foil shadow has been removed by the subtraction unit 24 is displayed on the monitor 15 or stored in the storage unit 16 via the main control unit 13.

As described above, according to the X-ray fluoroscopic imaging apparatus 1 of the first embodiment, the interpolation error included in calculating the approximate fluoroscopic image by averaging the foil shadow image reflected in the X-ray detection pixel DU in the vertical direction. Furthermore, it is possible to obtain a highly accurate foil shadow image from which amplifier noise and quantum noise have been removed. As a result, the foil shadow of the synchronous grid can be removed from the fluoroscopic image without causing artifacts to appear.

Furthermore, when the SID or the C-arm 5 is moved, even when the foil shadow moves from the X-ray detection pixel DU arranged in advance so that the foil shadow is reflected to the adjacent detection pixel, the foil shadow does not appear. Since the foil shadow image is obtained by approximating the fluoroscopic image by interpolation from the pixel set obtained by extracting the pixels for which the image has been determined, the foil shadow can be accurately removed. Thus, even when the X-ray tube focal point is accompanied by a minute uncontrollable movement, the foil shadow can be sufficiently removed. As a result, both the case where the foil shadow does not move across the pixels and the case where the foil shadow moves can be appropriately interpolated, and the X-ray sensitivity is about 20% higher than that of the conventional grid. Due to the effect of the grid, an image that exceeds the signal-to-noise ratio can be acquired.

Further, since the synchronous grid 3 and the radiation detector (FPD4) are arranged so that the foil shadows are projected in advance every four pixels, they are arranged so that the grid foils are projected in advance even if the foil shadows move. Since the movement of the foil shadow falls within the pixels on both sides of the pixel, a pixel in which the foil shadow is not necessarily reflected can be configured.

Next, Embodiment 2 of the present invention will be described with reference to FIG. 16 and FIG. FIG. 16 is a block diagram illustrating a configuration of an image processing unit according to the second embodiment, and FIG. 17 is a flowchart illustrating a flow of foil shadow correction processing according to the second embodiment. In FIG. 16 and FIG. 17, since the part shown with the code | symbol same as the code | symbol shown in Example 1 is the structure similar to Example 1, description here is abbreviate | omitted. In the second embodiment, the subtracting unit of the first embodiment is changed. Therefore, the structure of the X-ray fluoroscopic apparatus other than that described here is the same as that of the first embodiment.

The feature of Example 2 is that the foil shadow is removed by frequency conversion. The image processing unit 25 includes a LOG conversion unit 17, an image memory unit 18, a correction mode selection unit 19, a first approximate perspective image calculation unit 20, a second approximate perspective image calculation unit 21, a foil shadow image calculation unit 22, and a foil shadow standard. In addition to the image calculation unit 23, a foil shadow removal image calculation unit 33 is provided that removes the grid foil shadow from the perspective image based on the grid foil shadow standard image to obtain a foil shadow removal image.

The foil shadow removal image calculation unit 33 includes an error component image calculation unit 34 that calculates an error component image based on the difference between the grid foil shadow image and the grid foil shadow standard image, and an X-ray detection stored in the image memory unit 18. A foil shadow distortion removal image calculation unit 35 that calculates a foil shadow distortion removal image from which the foil shadow distortion has been removed by the difference between the image and the error component image, and the foil shadow distortion removal image by performing frequency conversion processing on the foil shadow distortion removal image. And a frequency conversion processing unit 36 for calculating a removal X-ray detection image.

The error component image calculation unit 34 calculates an error component image based on the difference between the grid foil shadow image and the grid foil shadow standard image. That is, it is possible to calculate the variation of the foil shadow based on the nonuniform shape for each grid foil 3a with reference to the ideal foil shadow image in the grid foil shadow image.

The foil shadow distortion-removed image calculation unit 35 calculates a foil shadow distortion-removed image from which the foil shadow distortion has been removed by the difference between the X-ray detection image stored in the image memory unit 18 and the error component image. Thereby, the variation in the detected value of the foil shadow due to the shape distortion of each grid foil 3a is corrected. That is, it can be said that all the foil shadows in the foil shadow distortion-removed image are ideal grid foil shadows, and the foil shadow sizes are uniform.

The frequency conversion processing unit 36 performs a frequency conversion process on the foil shadow distortion removed image to calculate a foil shadow removed fluoroscopic image. Since the foil shadow distortion-removed image is an image in which a foil shadow whose variation is corrected is superimposed on the fluoroscopic image of the subject, the foil shadow can be removed by performing a frequency conversion process. Thus, a fluoroscopic image of the subject from which the foil shadow has been removed can be acquired.

The fluoroscopic image of the subject from which the foil shadow has been removed by the frequency conversion processing unit 36 is displayed on the monitor 15 or stored in the storage unit 16 via the main control unit 13.

Next, the operation when X-ray fluoroscopic imaging is performed according to the second embodiment will be described. Steps S01 to S04 are the same as those in the first embodiment, and a description thereof will be omitted.

Step S15 (error component image calculation)
The error component image calculation unit 34 calculates an error component image based on the difference between the grid foil shadow image and the grid foil shadow standard image. That is, the variation of the foil shadow for each grid foil 3a with respect to the ideal foil shadow image in the grid foil shadow image is calculated.

Step S16 (calculate foil shadow distortion removed image)
The foil shadow distortion removed image calculation unit 35 calculates a foil shadow distortion removed image from which the foil shadow distortion has been removed based on the difference between the X-ray detection image stored in the image memory unit 18 and the error component image. Thereby, the variation in the detected value of the foil shadow due to the distortion of the grid foil 3a is corrected.

Step S17 (frequency conversion process)
The frequency conversion processing unit 36 performs a frequency conversion process on the foil shadow distortion-removed image to calculate a foil shadow removal perspective image. The foil shadow distortion-removed image is an image obtained by superimposing a uniform foil shadow whose variation is corrected on the fluoroscopic image of the subject. Therefore, the foil shadow can be removed by performing a frequency conversion process. Thus, a fluoroscopic image of the subject from which the foil shadow has been removed can be acquired.

As described above, according to the X-ray fluoroscopic imaging apparatus 1 of the second embodiment, the foil shadow image reflected on the X-ray detection pixel DU is averaged in the vertical direction, so that the amplifier noise and the quantum noise are removed and the accuracy is high. A foil shadow image can be obtained. Furthermore, since the error component image, which is the difference between the foil shadow image and the averaged foil shadow standard image, is differentiated from the fluoroscopic image by the foil shadow distortion removal image calculation unit 35, the foil shadows of all the grid foils 3a are uniform, The foil shadow can be removed by frequency conversion. Thus, the foil shadow of the synchronous grid can be removed without causing an artifact to appear.

Next, Embodiment 3 of the present invention will be described with reference to FIG. 18, FIG. 19, and FIG. 18 is a block diagram illustrating a configuration of an image processing unit according to the third embodiment. FIG. 19 is an explanatory diagram illustrating image processing according to the third embodiment. FIG. 20 illustrates foil shadow correction processing according to the third embodiment. It is a flowchart figure which shows a flow. 18, 19, and 20, the portions denoted by the same reference numerals as those of the first embodiment have the same configuration as that of the first embodiment, and thus the description thereof is omitted here. In the third embodiment, the calculation of the grid foil shadow standard image of the first embodiment is changed. Therefore, the structure of the X-ray fluoroscopic apparatus other than that described here is the same as that of the first embodiment.

In Example 1 described above, the standardization of the foil shadow averaged the pixel values in the vertical direction. Alternatively, the pixel values in the horizontal direction, which is the row direction, may be extracted every four pixels, and the extracted image data may be smoothed. For example, as shown in FIG. 18, the foil shadow standard image averaged in the vertical direction by the foil shadow standard image calculation unit 23 is converted into a constant by the smoothing unit 37, this time with the grid foil 3 a arranged in the horizontal direction. Each pixel in each row is extracted every four pixels, which is the number of pixels corresponding to the length of the gap (Gp). That is, as shown in FIG. 19A, by extracting pixels every four pixels in each row, row data in which pixel values are picked up for every four pixels is created.

More specific description will be given with reference to FIG. When the pixel values in the r-th row of the foil shadow standard image are Pr, 1, Pr, 2, Pr, 3,..., The pixel values in the r-th row are extracted every four pixels and shown in FIG. Thus, row data divided into four rows of r row-A, r row-B, r row-C, and r row-D are created. The image data of r-row-A, r-row-B, r-row-C, and r-row-D are every four pixel values of the original r-row image data.

The original row data has relatively large fluctuations, but the four new row data (r row-A, r row-B, r row-C, r row-D) have smooth values with little fluctuation. The four row data having pixel values are smoothed for every four pixels. Furthermore, by replacing the four smoothed row data (r row-A, r row-B, r row-C, r row-D) with the original foil shadow standard image data, Can remove amplifier noise and quantum noise from a fluoroscopic image that cannot be smoothed. In addition, in this processing step, as shown in FIG. 20, the smoothing step of step S21 is performed after the foil shadow standard image calculating step of step S4.

In the smoothing step, four row data are generated by extracting pixel values from the foil shadow standard image every four pixels within a predetermined interval in which the grid foil is arranged for each row, and each row data is smoothed. . Further, the four smoothed line data are replaced with the original foil shadow standard image. In addition, when the pixel in the fixed space | interval with which the grid foil 3a is arrange | positioned is set to the pixel number of 4 pixels or more, the row data for every set pixel number are created, and it smoothes.

Next, Embodiment 4 of the present invention will be described with reference to FIGS. FIG. 21 is a block diagram illustrating a configuration of an image processing unit according to the fourth embodiment, and FIG. 22 is a flowchart illustrating a flow of foil shadow correction processing according to the fourth embodiment. 21 and FIG. 22, the parts denoted by the same reference numerals as those shown in the first to third embodiments have the same configuration as that of the first to third embodiments, and thus the description thereof is omitted here. In the fourth embodiment, the calculation of the grid foil shadow standard image of the second embodiment is changed. Therefore, the structure of the X-ray fluoroscopic apparatus other than that described here is the same as that of the second embodiment.

In Example 2 described above, the standardization of foil shadows averaged the pixel values in the vertical direction. Alternatively, the pixel values in the horizontal direction, which is the row direction, may be extracted every four pixels, and the extracted image data may be smoothed. For example, as shown in FIG. 21, the foil shadow standard image averaged in the vertical direction by the foil shadow standard image calculation unit 23 is converted into a constant by the smoothing unit 31 and the grid foil 3 a in the horizontal direction. Each pixel in each row is extracted every four pixels within the interval. That is, as shown in FIG. 19, by extracting pixels every four pixels in each row, row data in which pixel values are picked up for every four pixels is created.

The original line data has relatively large fluctuations, but the four new line data have smooth values with little fluctuation. The four row data having pixel values are smoothed for every four pixels. Furthermore, by replacing the four smoothed line data with the original foil shadow standard image data, it is possible to remove amplifier noise and quantum noise from a fluoroscopic image that cannot be smoothed in the horizontal direction as it is. . Also, in this processing step, as shown in FIG. 22, the smoothing step of step S31 is performed after the foil shadow standard image calculating step of step S4.

The present invention is not limited to the above embodiment, and can be modified as follows.

(1) In the embodiment described above, one grid foil 3a is arranged for four pixels, but the present invention is not limited to this. In the embodiment, on the basis of four pixels, one pixel set to reflect a foil shadow, two pixels that the foil shadow may move, and one pixel that does not move the foil shadow at all. However, the present invention is not limited to this, and based on 8 pixels, 2 pixels set so that a foil shadow may appear, 4 pixels that the foil shadow may move, and 2 pixels that have no movement of the foil shadow may be used. Thus, the foil shadow correction mode can be further subdivided according to the amount of movement of the SID and the amount of movement of the C-arm 5, and the approximation accuracy of the approximate fluoroscopic image can be improved. The basic pixels are not limited to 4 pixels and 8 pixels, and may be 4 pixels or more. It is sufficient that there are four or more pixels and there is a pixel that is not affected by the movement of the foil shadow between the grid foils 3a.

(2) In the above-described embodiment, the detected digital X-ray detection signal is LOG-converted. However, if there is a margin in the arithmetic processing, the calculation may be performed without performing the LOG-conversion.

(3) In the embodiment described above, the correction mode selection unit 19 determines whether the first approximate image calculation or the second approximate image calculation is performed based on the SID amount set and input to the input unit 14 and the movement amount of the C-arm 5. Although the automatic selection is performed, a configuration in which the operator can select which correction mode by the input unit 14 may be used. It is also possible to always calculate and use the second approximate image without selecting the correction mode. As a method of selecting the correction mode from the SID amount and the movement amount of the C-shaped arm 5, both values are changed in advance, an image is taken without placing the subject M on the top 8, and selected from the pattern of foil shadows. It is only necessary to determine the correction mode to be performed.

(4) In the above-described embodiment, pixels that are not affected by the foil shadow are extracted based on the arrangement of the pixels arranged so that the foil shadow is projected in advance. A pixel set that is not affected by other foil shadows may be extracted by detecting pixels in which the foil shadows are reflected. In this way, a pixel in which a foil shadow is reflected by image processing may be detected, and switching between the normal correction mode and the special correction mode may be performed based on the result. In the case of the special correction mode, a pixel set obtained by extracting pixels adjacent to the pixel in which the center of the foil shadow is reflected may be employed.

Claims

In the grid foil shadow removal method of the radiation imaging apparatus including the synchronous grid in which the grid foil is arranged at a constant interval so that the grid foil shadow is reflected in the center of the pixel detecting the radiation,
An approximate perspective image calculation step for obtaining an approximate perspective image by extracting a detection signal value of a pixel not affected by the grid foil shadow from the perspective image and performing an interpolation process;
A grid foil shadow image calculating step for obtaining a grid foil shadow image by obtaining a difference between the perspective image and the approximate perspective image;
Foil shadow standard image calculation step for obtaining the foil shadow standard image by averaging the grid foil shadow image in the length direction of the grid foil shadow;
And a foil shadow removal step of removing the grid foil shadow from the fluoroscopic image based on the foil shadow standard image.
In the grid foil shadow removal method of Claim 1,
The method of removing a foil foil shadow includes removing the grid foil shadow from the fluoroscopic image based on a difference between the fluoroscopic image and the foil shadow standard image.
In the grid foil shadow removal method of Claim 2,
Foil shadow standard image averaged by the foil shadow standard image calculation step, for each row, to create a row data divided by extracting and dividing for each number of pixels within a certain interval where the grid foil is disposed, A smoothing step of smoothing the line data to replace the original foil shadow standard image,
The foil shadow removal step of removing the grid foil shadow from the fluoroscopic image based on a difference between the fluoroscopic image and the smoothed foil shadow standard image.
The grid foil shadow removal method according to claim 1, wherein the foil shadow removal step comprises:
An error component image calculation step for obtaining an error component image by obtaining a difference between the grid foil shadow image and the foil shadow standard image;
Foil shadow distortion removed image calculation step for obtaining a difference between the perspective image and the error component image to obtain a foil shadow distortion removed image;
A frequency foil processing step of performing a frequency conversion process on the foil shadow distortion-removed image to remove the grid foil shadow, and a grid foil shadow removal method.
In the grid foil shadow removal method of Claim 4,
Foil shadow standard image averaged by the foil shadow standard image calculation step, for each row, to create a row data divided by extracting and dividing for each number of pixels within a certain interval where the grid foil is disposed, A smoothing step of smoothing the line data to replace the original foil shadow standard image,
The method of calculating a grid foil shadow, wherein the error component image calculation step calculates an error component image by calculating a difference between the grid foil shadow image and the smoothed foil shadow standard image.
In the grid foil shadow removal method according to any one of claims 1 to 5,
Image processing for selecting either the normal correction mode in which the movement of the foil shadow between the pixels is not corrected or the special correction mode in which the movement of the foil shadow between the pixels is corrected based on the input SID amount and the movement amount of the C-shaped arm A mode selection step;
When the normal correction mode is selected in the image processing mode selection step, the approximate perspective image calculation step extracts and interpolates the detection signal values of all the pixels other than the pixels arranged in advance so that the grid foil shadow is reflected. Process,
When the special correction mode is selected in the image processing mode selection step, the approximate perspective image calculation step calculates the detection signal value of the pixel located at the center between the grid foils where the foil shadow does not appear even if the foil shadow moves. A grid foil shadow removal method characterized by extracting and performing interpolation processing.
In radiography equipment,
Radiation irradiation means for irradiating the subject with radiation;
Radiation detecting means in which pixels for detecting radiation transmitted through the subject are arranged in a two-dimensional array;
A synchronous grid arranged at regular intervals so that a grid foil shadow is reflected in the center of the pixel;
An approximate fluoroscopic image calculation unit that extracts a set of pixels that are not affected by the grid foil shadow from a fluoroscopic image detected through the subject and performs an interpolation process to calculate an approximate fluoroscopic image;
A grid foil shadow image calculation unit for obtaining a grid foil shadow image by obtaining a difference between the perspective image and the approximate perspective image;
A foil shadow standard image calculating unit that averages the grid foil shadow image in the length direction of the grid foil shadow to obtain a grid foil shadow standard image;
A radiation imaging apparatus comprising: a foil shadow removal image calculation unit that obtains a foil shadow removal image by removing the grid foil shadow from the fluoroscopic image based on the grid foil shadow standard image.
The radiation imaging apparatus according to claim 7,
The radiographic apparatus according to claim 1, wherein the foil shadow removal image calculation unit obtains the foil shadow removal image based on a difference between the fluoroscopic image and the grid foil shadow standard image.
The radiation imaging apparatus according to claim 7,
The foil shadow removal image calculation unit,
An error component image calculation unit for obtaining an error component image by obtaining a difference between the grid foil shadow image and the grid foil shadow standard image;
A foil shadow distortion removed image calculating unit for obtaining a difference between the perspective image and the error component image to obtain a foil shadow distortion removed image;
A radiation imaging apparatus comprising: a frequency conversion processing unit that performs frequency conversion processing on the foil shadow distortion-removed image to remove grid foil shadows.
The radiographic apparatus according to any one of claims 7 to 9,
An input unit for inputting and setting the SID amount and the movement amount of the C-shaped arm;
A correction mode selection unit that selects either the normal correction mode or the special correction mode based on the input SID amount and the movement amount of the C-arm,
When the normal correction mode is selected as the correction mode, the approximate perspective image calculation unit extracts the detection signal values of all the pixels other than the pixels previously arranged so that the grid foil shadow is reflected, and performs an interpolation process. When the special correction mode is selected as the correction mode, the detection signal value of the pixel located at the center between the grid foils where the foil shadow does not appear even if the foil shadow moves is extracted and interpolation processing is performed. Radiation imaging device.
The radiographic apparatus according to any one of claims 7 to 10,
The foil shadow standard image calculated by the foil shadow standard image calculation unit is created for each row, creating row data divided by extracting for each number of pixels within a predetermined interval where the grid foil is arranged, and A radiation imaging apparatus comprising a smoothing unit that smoothes line data and replaces the original foil shadow standard image.
The radiation imaging apparatus according to any one of claims 7 to 11,
The radiographic apparatus according to claim 1, wherein the synchronous grid and the radiation detector are arranged in advance so that a grid foil shadow is reflected every four pixels.